1. Field of the Invention
This application claims the benefit of Japanese Patent Application No. 2008-195701, filed Jul. 30, 2008, which is hereby incorporated by reference herein in its entirety.
2. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine or a printer, which functions to form an image on a recording medium of a sheet.
3. Description of the Related Art
Normally, a fixing unit which fixes a toner image transferred onto the sheet by applying heat and pressure is provided in an image forming apparatus which utilizes electrophotography such as a laser-beam printer. The fixing unit is arranged at the downstream side of an image transfer portion of the image forming apparatus and is provided with a pressure roller and a heat unit. Then, the pressure roller and the heat unit are press-contacted to each other so as to form a nip. The toner image is fixed onto the sheet by applying pressure and heat when the sheet passes through the nip.
In order to fix the toner image, considerable pressing force is required. In general, the press-contacting force between the pressure roller and the heat unit is larger than that of other sheet conveying rollers. Therefore, when a sheet jam occurs at the fixing unit, jam recovery may be difficult due to the large pressing force. Thus, there may be problems from fragments of a torn sheet that are difficult to dispose and from the risk of destroying a member since the jam recovery is required to be performed with large force.
Accordingly, mechanisms which interconnect the release of pressing force for fixing with opening of an opening and closing door for performing the jam recovery have been proposed.
For example, a mechanism with which load to an opening and closing door is decreased by utilizing a linkage when the pressure releasing of the fixing unit is performed being interlocked with operation of the opening and closing door has been proposed in Japanese Patent Application Laid-open (JP-A) No. 2002-148992. Further, a link connection mechanism with which the fixing unit is easily detached and attached by simplifying engagement of a pressure release linkage of the fixing unit with the opening and closing door has been proposed in JP-A No. 2007-079488. In addition, an image forming apparatus which utilizes a linkage has been proposed in JP-A Nos. 2006-047647 and 2008-164781, and a process cartridge which utilizes a linkage has been proposed in JP-A No. 2007-047298.
However, with a pressure release mechanism which utilizes gears, the mechanism cannot be operated properly when a phase of the attached gears is shifted. In particular, since the fixing unit is a unit which may be replaced by a serviceman in the field, the gears need to be assembled at a predetermined phase when the fixing unit is attached or detached.